[Binding of Ca2+ ions to bovine alpha-lactalbumin. Intrinsic protein fluorescence changes].
Binding of Ca2+ ion to bovine alpha-lactalbumin molecule causes a conformational change reflected in an almost two-fold decrease of the fluorescence quantum yield and a rather pronounced spectral shift towards shorter wavelengths (by ca. 20 nm). The changes could be interpreted as a result of a transfer of highly exposed tryptophan residue(s) into a rigid internal part of the protein molecule containing effective quenching groups (probably, vicinal disulphide bridges). The Ca2+ binding constant evaluated from EGTA--and pH-titrations is (3-6) X 10(8) M-1. The results of the spectrofluorometric pH-titration of alpha-lactalbumin in the presence of various Ca2+ concentrations suggest that the well-known acid conformational change in alpha-lactalbumin is due in fact to a competitive replacement of the bound Ca2+ by three H+ ions (pK = 5.0 +/- 0.1) in the Ca2+ binding site.
D000818:Animals; D002118:Calcium; D002417:Cattle; D004533:Egtazic Acid; D006863:Hydrogen-Ion Concentration; D007768:Lactalbumin; D011485:Protein Binding; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence
D004533:Egtazic Acid; D007768:Lactalbumin; D002118:Calcium
Sviazyvanie ionov Ca2+ al'fa-laktal'buminom iz korov'ego moloka. Issledovanie po izmeneniiam sobstvennoĭ belkovoĭ fluorestsentsii.